class Terminal::Table::Row

we only care about "+/T" style crossings.
skip last entry, because it's the right side.
skip 0 entry, because it's the left side.

if colspan is always 1, then the list should be incrementing by 1.
in cases where the colspan > 1, then we will skip over some numbers
used to find indices where we have table '+' crossings.

def crossings
  idx = 0
  @cells[0...-1].map { |c| idx += c.colspan } 
end